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PROTEIN PROTEIN SYNTHESISSYNTHESIS
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DNA DNA and and
GeneGeness
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DNADNA•DNA contains genes,
sequences of nucleotide bases
•These Genes code for polypeptides (proteins)
•Proteins are used to build cells and do much of the work inside cells
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Genes & ProteinsGenes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
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Amino Acid Amino Acid StructureStructure
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PolypeptidesPolypeptides
•Amino acid chains are called polypeptides
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DNA Begins the DNA Begins the ProcessProcess
• DNA is found inside the nucleus
• Proteins, however, are made in the cytoplasm of cells by organelles called ribosomes
• Ribosomes may be free in the cytosol or attached to the surface of rough ER
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Starting with DNAStarting with DNA• DNA ‘s codeDNA ‘s code must be must be copiedcopied
and taken to the cytosoland taken to the cytosol• In the cytoplasm, this In the cytoplasm, this code code
must be readmust be read so so amino acidsamino acids can be assembled to make can be assembled to make polypeptides (proteins)polypeptides (proteins)
• This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS
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RNARNA
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Roles of RNA and DNA•DNA is the MASTER
PLAN
•RNA is the BLUEPRINT of the
Master Plancopyright cmassengale
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RNA Differs from DNARNA Differs from DNA• RNA has a sugar RNA has a sugar riboseribose
DNA has a sugar DNA has a sugar deoxyribosedeoxyribose
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Other DifferencesOther Differences• RNA contains RNA contains
the base the base uracil uracil (U(U))DNA has DNA has thymine (T)thymine (T)
• RNA molecule is RNA molecule is single-strandedsingle-strandedDNA is DNA is double-double-strandedstranded
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Structure of RNAStructure of RNA
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. Three Types of Three Types of RNARNA
• Messenger RNA (mRNA)Messenger RNA (mRNA) copies copies DNA’s code & carries the DNA’s code & carries the genetic information to the genetic information to the ribosomesribosomes
• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), along , along with protein, makes up the with protein, makes up the ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are synthesizedwhere proteins are synthesized
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Messenger RNA• Long Straight chain
of Nucleotides• Made in the
Nucleus• Copies DNA &
leaves through nuclear pores
• Contains the Nitrogen Bases A, G, C, U ( no T )
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Messenger RNA (mRNA)Messenger RNA (mRNA)• Carries the information for a Carries the information for a
specific proteinspecific protein• Made up of Made up of 500 to 1000 500 to 1000
nucleotides longnucleotides long• Sequence of 3 bases called Sequence of 3 bases called
codoncodon• AUGAUG – methionine or – methionine or start codonstart codon• UAA, UAG, or UGAUAA, UAG, or UGA – – stop codonsstop codons
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Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)• rRNA is a single rRNA is a single
strand strand 100 to 100 to 3000 nucleotides3000 nucleotides longlong
• GlobularGlobular in shape in shape• Made inside the Made inside the
nucleusnucleus of a cell of a cell• Associates with Associates with
proteins to form proteins to form ribosomesribosomes
• Site of Site of protein protein SynthesisSynthesis
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The Genetic Code• A codon designates an
amino acid• An amino acid may have
more than one codon• There are 20 amino acids,
but 64 possible codons• Some codons tell the
ribosome to stop translating
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The Genetic Code •Use the
code by reading from the center to the outside•Example: AUG codes for Methionine
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Name the Amino Acids
•GGG?•UCA?•CAU?•GCA?•AAA?
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Remember the Remember the Complementary Complementary
BasesBasesOn DNA: A-T C-GOn RNA: A-U C-G
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Transfer RNA Transfer RNA (tRNA)(tRNA)
• Clover-leaf shape• Single stranded molecule
with attachment site at one end for an amino acid
• Opposite end has three nucleotide bases called the anticodon
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Transfer RNATransfer RNAamino acidamino acid
attachment siteattachment site
U A C
anticodonanticodoncopyright cmassengale
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Codons and Anticodons
• The 3 bases of an anticodon are complementary to the 3 bases of a codon
• Example: Codon ACU
Anticodon UGA
UGA
ACU
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TranscriptiTranscription and on and
TranslationTranslation
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Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProteincopyright cmassengale
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Protein SynthesisProtein Synthesis The production or synthesis of
polypeptide chains (proteins) Two phases:
Transcription & Translation mRNA must be processed
before it leaves the nucleus of eukaryotic cells
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DNADNA RNARNA ProteinProteinNuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
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TranscriptionTranscription•The process of copying
the sequence of one strand of DNA, the template strand
•mRNA copies the template strand
•Requires the enzyme RNA Polymerase
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Template Strand
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Question:Question: What would be the What would be the
complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’copyright cmassengale
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Answer:Answer:•DNA 5’-GCGTATG-DNA 5’-GCGTATG-3’3’
•RNA 3’-CGCAUAC-RNA 3’-CGCAUAC-5’5’
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TranscriptionTranscription• During transcription, RNA
polymerase binds to DNA and separates the DNA strands
• RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA
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TranscriptionTranscription• Promoters are regions on
DNA that show where RNA Polymerase must bind to begin the Transcription of RNA
• Called the TATA box• Specific base sequences act
as signals to stop• Called the termination signal
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RNA PolymeraseRNA Polymerase
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mRNA ProcessingmRNA Processing•After the DNA is
transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
• Introns, non-functional segments of DNA are snipped out of the chain
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mRNA EditingmRNA Editing• Exons, segments of DNA that code for proteins, are then rejoined by the
enzyme ligase• A guanine triphosphate cap is added to the 5” end of the newly copied mRNA• A poly A tail is added to the 3’ end of the RNA• The newly processed mRNA can then leave the nucleus
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TailNew Transcript
Result of TranscriptionResult of Transcription
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mRNA Transcript•mRNA leaves the nucleus through its pores and goes to the ribosomes
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TranslationTranslation•Translation is the process
of decoding the mRNA into a polypeptide chain
•Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
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TranscriptioTranscriptionn
TranslatiTranslationon
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RibosomesRibosomes•Made of a large and
small subunit•Composed of rRNA
(40%) and proteins (60%)
•Have two sites for tRNA attachment --- P and A
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Step 1- InitiationStep 1- Initiation• mRNA transcript
start codon AUG attaches to the small ribosomal subunit
• Small subunit attaches to large ribosomal subunit
mRNA transcriptcopyright cmassengale
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RibosomesRibosomes
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C Gcopyright cmassengale
Step 2 - Elongation• As ribosome moves, two tRNA
with their amino acids move into site A and P of the ribosome
• Peptide bonds join the amino acids
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InitiationInitiation
mRNAmRNAA U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodonhydrogen
bonds codoncopyright cmassengale
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mRNAmRNAA U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodonhydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3ElongationElongation
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mRNAmRNAA U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
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mRNAmRNAA U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
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mRNAmRNAA U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codoncopyright cmassengale
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mRNAmRNAG C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
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mRNAmRNAG C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codoncopyright cmassengale
53mRNAmRNAA C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
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End Product –The End Product –The Protein!Protein!
• The end products of protein synthesis is a primary structure of a protein
• A sequence of amino acid bonded together by peptide bonds
aa1
aa2 aa3 aa4aa5
aa200
aa199
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Messenger RNA Messenger RNA (mRNA)(mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
startcodon
Primary structure of a proteinPrimary structure of a proteinaa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
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